Background
Patients with systemic lupus erythematosus (SLE) experience an increased risk of cancer, which is particularly driven by hematological malignancies. Our objective was to determine whether certain factors (demographics, SLE duration and calendar year) were associated with cancer risk in SLE, relative to the general population, using a large multicenter clinical cohort.
Methods
We present detailed analyses of a multisite international SLE cohort (30 centers, 16,409 patients). Cancers were ascertained by registry linkage. Standardized incidence ratios (SIR; ratio of observed to expected cancers) were calculated for overall and for hematological cancer risk, representing the relative risk of cancer for SLE patients, versus the age, sex, and calendar-year-matched general. We used Poisson hierarchical regression to assess for potential independent effects of the factors examined (sex, race/ethnicity, age group, SLE duration, calendar-year period) on the SIRs among the SLE cohort members. The hierarchical nature of the model allowed for differences in effects from one country to the next.
Results
In adjusted analyses (Table 1), we demonstrated lower SIR estimates for overall cancer risk, in black versus white SLE patients, in SLE patients of older versus younger age, and for patients with SLE duration of 5 years or more (versus lower duration). Female sex and calendar year were not clearly associated with any differences in the SIR estimates for SLE patients. Regarding hematological cancer specifically, SLE duration of 5 years or more again appeared to be associated with lower SIR estimates.
Table 1.
Results of adjusted multivariate regression to determine independent effect of variables on SIR* estimates for cancer in SLE
| Adjusted effectsa | 95% confidence interval | |
|---|---|---|
| Female sex | 1.00 | 0.77 to 1.30 |
| Race/ethnicity | ||
| White | Reference group | |
| Black | 0.75 | 0.58 to 0.97 |
| Asian | 1.18 | 0.85 to 1.62 |
| Age | ||
| <40 | Reference group | |
| 40 to 59 | 0.72 | 0.55 to 0.94 |
| 60+ | 0.55 | 0.42 to 0.73 |
| SLE duration | ||
| <5 years | Reference group | |
| ≥5 years | 0.74 | 0.61 to 0.89 |
| Calendar-year period | ||
| <2000 | Reference group | |
| ≥2000 | 0.95 | 0.79 to 1.15 |
aVariables adjusted concomitantly for all others (sex, race/ethnicity, age, SLE duration, calendar-year period).
Conclusions
Although cancer risk in SLE is increased relative to the general population, patients most at risk appear to be those of white race/ethnicity, younger age, and of shorter SLE duration.